Based on the discovery of the radical mediated [3+2] methylenecyclopentane annulation of unactivated and electron-rich olefins with 2-phenylsulfonylmethylene-cyclopropanes, this proposal aims to develop new free-radical mediated annulation and addition reactions. Toward that end, the initial objective will be to develop a series of [3+2] annulation reagents allowing the methylenecyclopentane annulation of unactivated and electron-rich olefins, and a new class of methylenecyclopentane annulations of electron-poor olefins. Another objective is to develop new addition reactions of unactivated olefins using alpha-sulfonyl radicals. A final objective is to develop, for the first time, methods for the catalytic control of the absolute and relative stereochemistry of some radical cyclizations. The health relatedness of the project derives from its impact on methods for the synthesis of a wide variety of medicinally important natural and artificial substances.